Compression therapies may be used for treatment and/or prophylaxis of a number of conditions, including, but not limited to, Deep Vein Thrombosis (DVT), vascular disorders, circulatory disorders, edemas, heart conditions (treated by counterpulsation), lymphedema, burns and embolisms. Other areas of use may be stress therapy, massage therapy, blood pressure monitoring, fit adjustment mechanisms for prostheses and suits for preventing pooling of blood in body parts of pilots or race car drivers subjected to G-forces.
US 2004/0073146 A1 discloses a portable device for enhancing blood flow in a limb with a view to decreasing the risk of developing a Deep Vein Thrombosis. The device comprises a strap, which is wound around the limb, and a housing comprising a motor, which is arranged pull the strap by a reciprocating motion, such that a compressive force is applied to the limb.
The motor of US 2004/0073146 A1 is of an electromagnetic type, which provides low power to weight ratio, and thereby a very bulky device. When combined with the low efficiency of the disclosed motors and power transmission elements, the result is a short battery life. Furthermore, the device would require a complex locking mechanism for holding the pressure during a period longer than that of the reciprocating motion. Also, due to the torque capabilities of conventional electromagnetic motors, it would be difficult to meet the force requirements for Deep Vein Thrombosis prophylaxis using this technology and in a compact format. Furthermore, as the reciprocating motion is produced through an intermediate mechanism and the tissue mechanics of every patient are different, there will be little to no control of the actual force output applied by the straps onto the patient.
US 2002/0173735 A1 discloses a device for external counter pulsation treatment of a heart disease or circulatory disorder. The device comprises a cuff, which is to be wrapped around a patient's extremity. The ends of the cuff are attached to each other such that electrical activation of actuators of the cuff will cause it to constrict. The actuators may be solenoid actuators, which typically provide a reciprocating motion.
The device of US 2002/0173735 A1 is only suitable for impulse applications, since the solenoid actuator cannot be made to retain a force for a period longer than that of the reciprocating motion, since a very high current would be required to provide for low frequency or static operation. This device also provides low power to weight ratio, resulting in a heavy device. Furthermore, the device is only capable of providing small motions, due to the tight fitting requirements of the cuff.
Furthermore, solenoid actuators are only capable of providing small motions, thereby placing tight fitting requirements on the cuff. Motion limitations of the actuators will also limit the actual forces that one can apply to the patient as the patient's tissue compliance will have to be overcome to reach significant force levels.
U.S. Pat. No. 6,494,852 B1 discloses a portable ambulant pneumatic compression device, comprising a sleeve having inflatable cells, which are coupled to a conduit delivering a fluid from a control device.
The use of pneumatic actuation as disclosed in U.S. Pat. No. 6,494,852 B1 also provides low power to weight ratio and thereby makes the device bulky. Furthermore, efficiency of pneumatic devices is low, as they waste much energy in their compressors, valves, accumulators, conduits, and bladder expansion, in addition to wasting energy on each deflation cycle by venting the compressed air to the surroundings. Hence, such a device requires an oversized power unit and will provide short battery lives. The use of pneumatic bladders also results in bulky, non-breathable garments around the patient's limb.
Compression devices having straps or cuffs comprising active material, that are intended to be wound around a body part, are illustrated in U.S. Pat. No. 5,997,465, U.S. Pat. No. 6,123,681, U.S. Pat. No. 6,198,204 B1, EP 1 324 403 A1, US 2004/0167375 A1, WO 2004/093763 A1 and US 2005/0043657 A1. These devices generally require large amounts of active material, and are therefore at present only suitable for high-cost applications. Some of the concepts shown in these documents also require active materials having properties that cannot be achieved in large scale production or cannot be maintained over many actuation cycles with known materials.
Each of the configurations of the prior art would place undue burden on the active material properties. The materials are required to perform extreme combinations of stroke and force against patients, with widely varying geometry and tissue compliance. Therefore either excessive material or very high performance material is needed for the devices, leading to both high cost devices and increased reliability and safety issues in practical devices.
Hence, there is a need for an improved device for compression treatment of a body part.